1. Field of the Invention
This invention relates to a boring apparatus and more particularly to a boring apparatus for horizontally boring small diameter holes for cables or other utility lines under a street or sidewalk.
2. Description of the Prior Art
Augers are most commonly used to bore small diameter holes under streets or under sidewalks where it would be uneconomical or unfeasible to create a trench. The holes are made for the continuous laying of utility lines.
A commercially available tool for drilling such holes comprises an auger secured to the end of a bore line which is rotated by a motor. The bore line is most commonly set into the side of the earth so that the auger may bore a hole horizontally through the earth.
The auger is a one-piece metal tool having a small cutting edge at the front thereof. A conical-shaped threaded section extends from the cutting edge to an expander. The threaded section is radially larger toward the expander. The expander is a cylindrical surface of a diameter at least as great as that of the adjacent threaded section.
In addition, some conventional one-piece augers have an integrally-formed threaded section located behind the expander.
The cutting bit is used to cut through earth, such as clay or soil, and to create a small hole so the threaded section can engage the earth around the hole and thread its way into the earth like a corkscrew. As the auger threads through the earth, the threads create a continually larger diameter hole until the expander passes through the hole, thereby compacting the earth and expanding the hole. No earth is removed from the hole, but the earth is simply compressed about the hole. The rear-threaded section is used to thread the auger out of the hole if any cave-ins occur within the hole.
U.S. Pat. No. 2,979,141 issued to Kandle on Apr. 11, 1961, discloses a one-piece auger with a front cutting edge, a tapered screw flight for threading itself into the bored hole, and a cylindrical portion located behind the threads for compressing the sides of the hole as it passes therethrough. Behind the expander are means to connect the auger to the rotating drive shaft sections.
U.S. Pat. No. 3,550,698 issued to Pauley on Dec. 29, 1970, discloses an auger with a cutting head and integrally-formed helical screw flight which threads the auger forward through the earth.
Cutting edges and screw flights are found not only on augers, but also on drill bits which cut into hard rock. The cutting bit is braced onto a cylindrical shaft. The cutting bit has a radial length equal to the diameter of the cut hole. The screw flights are sometimes made from a resilient material which is threaded about the shaft such that when the shaft rotates, the threads conduct dust and dirt outwardly up and out of the drilled hole.
The problem encountered with augers are that one or more sections of the auger are liable to wear out or break through the repetitive rotation through earth, sand, and rock. Sometimes the cutting bit may wear out first, or the threads or the expander may wear out first, depending upon the speed of the rotation, the kind of soil which is being bored, and the number of cave-ins and obstacles met while the auger is boring through the earth. The relative hardness of the sections of the auger is also an important factor in determining which section wears out the fastest. When one of the sections becomes worn, the whole auger needs to be replaced.
In addition, the auger is a relatively complicated shaped tool with many curves and bends which militates against the use of hardened steel or other harder metals for the augers. It is well known that the more intricately shaped tools must be made from softer metals which can be machined or cast. Harder metals become economically unfeasible for use in augers since the machining of harder metals wear out the machining tools and equipment. As a consequence, the augers must be made from softer metals and are subject to more wear and tear and must be replaced more often than desirable.